1. Field of the Invention
The present invention relates to a structure for preventing oil from being contaminated, and more particularly to a structure for preventing oil contamination for a hydraulically operated power steering system of the rack-and-pinion type.
2. Description of the Relevant Art
Japanese Laid-Open Utility Model Publication No. 62-74075 published May 12, 1987 discloses a structure for preventing oil contamination for a hydraulically operated power steering system of the rack-and-pinion type. The disclosed structure includes a plurality of ring-shaped permanent magnets disposed at respective plural locations in a working oil chamber within the gear box of the steering system, with a rack extending through the ring-shaped permanent magnets. A pinion and grack teeth are held in mesh with each other in the gear box. Iron-base metal particles which may be produced by such meshing engagement between the pinion and the rack teeth are magnetically attracted to the permanent magnets thereby to prevent oil in the working oil chamber from being contaminated. As a result, oil leakage from seals and damage to sliding portions, which would otherwise be caused by entrapped metal particles, are prevented from occurring.
The rack is made of an iron-base material that can be magnetized, and the ring-shaped permanent magnets are disposed relatively closely to the rack. Therefore, the rack may possibly be magnetized by the permanent magnets to the extent that the rack itself may magnetically attract iron-base metal particles, thus lowering the ability of the permanent magnets to attract the iron-base metal particles. To solve this problem, the disclosed structure includes members of a nonmagnetic material such as synthetic resin, for example, which are disposed between the ring-shaped permanent magnets and the rack.
However, use of the nonmagnetic members of synthetic resin makes the oil contamination preventing structure somewhat complex in construction.
It would be preferable in efforts to provide a simpler and less expensive structure for preventing oil contamination if the conventional nonmagnetic members of synthetic resin were dispensed with.
The present invention has been made in an attempt to circumvent the aforesaid drawbacks of the conventional structure for preventing oil contamination for a hydraulically operated power steering system.